Method of making heat exchanger tube



Nov. 8, 1955 J. R. MEYER ET AL 2,722,733

METHOD OF MAKING HEAT EXCHANGER TUBE Filed Nov. 8, 1950 17174972 50715.Jamaal? W g/en era/W9. Laefi e5.

Unite States Patent NIETHOD OF MAKING HEAT EXCHANGER TUBE James R. Meyerand Frederick A. Loebel, Milwaukee,

Wis., assignors to Cleaver-Brooks Company, a corporation of WisconsinApplication November 8, 1950, Serial No. 194,628

1 Claim. (Cl. 29-1573) This invention relates to a heat exchanger tubeand more particularly to a new tube and the method in which it is made.

Space may be saved in heat exchangers, by providing an increase in heatexchange area within each tube to decrease the number of tubes necessaryto effect a given quantity of heat exchange. This may be accomplished byutilizing a tube having internal fins.

It is the principal object of this invention to provide a new andimproved heat exchanger tube, made by a new and improved method.

Another object is to provide a new and improved method for manufacturingan internally finned heat exchanger tube of commercially availablematerial without the aid of bonding agents between the tube and theinternal fins.

Another object is to provide a method of securing smaller tubes in sideby side relation within a larger tube to make an internally finned heatexchanger tube without the aid of bonding agents, and so that the largertube will have a positive sealed wide line of contact with each of thesmaller tubes through all operating temperatures to which the heatexchanger tube may be subjected.

Other objects and advantages will be apparent from the description of aparticular embodiment illustrated in the accompanying drawings in which:

Fig. 1 is an end view of an assembly of small tubes placed inside asingle larger tube with the inner tubes loosely in place; Fig. 2 is abroken side view, partly in section, of the tubes shown in Fig. 1; Fig.3 is a diagrammatic side view of a die through which the assembly ofFigs. 1 and 2 may be passed; Fig. 4 is an end view of the assembly afterit has passed through the die; Fig. 5 is a broken side view, partly insection, of the assembly shown in Fig. 4.

While we have shown and shall hereafter describe a certain embodiment ofour invention, it is to be understood that it is capable of manymodifications. Changes, therefore, in the construction and arrangementmay be made without departing from the spirit and scope of the inventionas disclosed in the appended claim.

Many heat exchangers employ a tube bundle within a shell arranged tohave a hot fluid pass around and between the tubes to heat a relativelycooler fluid passed through the tubes between headers on the shell. Theheat exchange is thus aflected by conduction through the walls of thetubes and it logically follows that, other things being the same, withgreater area available for conduction of heat will come greater heatexchange. Where, due to the nature of the fluids or other materials onthe two sides of the heat exchanger, it is desirable to increase theexposed area on the inside of a tube, this has sometimes beenaccomplished by employing internally finned tubes. This invention isconcerned with a new and improved tube of the internally finned type.

As shown in Figs. 1 and 2, three relatively small tubes 6 are placed inside by side relation so that their axes 2 ,722,733 Patented Nov. 8,1955 are mutually parallel. These tubes 6 are then placed within asingle larger tube 7 so that all the axes of the tubes are thenparallel. The sizes of the respective tubes 6 and 7 are so chosen thatthe smaller tubes may be easily inserted or withdrawn from the larger,yet substantially fill the larger without room for an additional tube 6of the same size. Generally, the tubes 6 are slightly shorter than thetube 7 so as to facilitate the necessary operations for installing andconnecting the tubes. It is contemplated that all of the space withinthe tube 7, both inside and around tubes 6, will contain the same fluidor other material, the tubes 6 through their contact with the tube 7acting as internal fins thereon.

In the embodiment shown, three small tubes have been placed within asingle larger tube. This number may vary according to the area of finsdesired within the larger tube 7.

After the tubes have been assembled as illustrated in Figs. 1 and 2, theassembly 9 may be passed through one or more dies 8 (Fig. 3). Each dieis tapered in the direction of the arrow to draw the outer tube 7 to asmaller diameter throughout its entire length. By contracting orreducing the diameter of the outer tube 7, the smaller tubes and outertube are drawn together along longitudinal lines of contact betweentheir walls. The assembly is reduced in diameter a suflicient amount tocause the inner tubes 6 to flatten along areas 10 along the line ofcontact of the tubes 6 and the outer tube 7, and along contacting lines11 between adjacent pairs of tubes 6. This flattening serves severalpurposes, in that it increases the area of intimately contacting metalbetween the tubes, thus increasing available surface between tubes forheat transfer by conduction, insures that an intimate contact is madebetween the tubes along the entire length of the tubes and that suchcontact is maintained during any expansion or contraction of the tubesdue to temperature changes. The tubes may have some resiliency impartedto their walls when the assembly is passed through the dies, thus makingthe inner tubes press against the outer tube to maintain intimatecontact.

It is important that the best possible heat transfer between the wallsof the outer tubes 7 and the fins formed by the inner tubes 6, beaccomplished. The tube of this invention is advantageous in this regard.The assembly 9 may be reduced in diameter uniformly along its entirelength, thus insuring intimate contact between all the tubes. Thedifficulty of brazing or soldering the tubes together is eliminated aswell as the uncertainty in making a good heat conductive union betweenthe tubes.

If it is desired that the outer diameter of the assembly remain the sameas the original size of the tube 7, one or more of the smaller tubes maybe expanded instead of reducing the diameter of the larger tube 7. Thismethod accomplishes the same result and the same resiliency may beimparted to the walls of the tubes to maintain the intimate contactbetween them.

As an example of the use of a tube make in accordance with thisinvention, a heat exchanger was equipped with 80, 1% tubes each havingthree internal smaller tubes and provided the same amount of availableheat transfer area as a much larger heat exchanger having 400, 1" tubes.The same size heat exchanger as the one containing 1' tubes would belarge enough to contain approximately 300, 1%" tubes. A great savings inspace was thus effected.

We claim:

The method of making a heat exchanger tube comprising, placing threeround cross section tubes of the same diameter within a single largertube so that the axes of all the tubes are parallel and each tube is incontact with all the others, then reducing the diameter of the largertube to force all the tubes into heat conductive contact throughintimately contacting wall surfaces and then stopping the reduction ofthe larger tube after the contacting portions of the tubes haveflattened to provide said contacting walls and before materiallychanging the size of the passages through the tubes.

Durr Oct. 23, 1900 Bennett Apr. 28, 1931 4 Kerr Sept. 20, 1932 Townsendet a1. Nov. 14, 1939 Aronson et a1 May 27, 1941 Bisch June 15, 1948Boling Sept. 23, 1952 Boling Sept. 23, 1952 Bergan Dec. 23, 1952Simpelaar Nov. 2, 1954 FOREIGN PATENTS Switzerland Jan. 17, 1944

